The Viral Epidemiology Branch has used a variety of approaches to define the nature and magnitude of HIV-1 associated malignancies, including analyses of population-based cancer registries, death certificates, prospective cohorts, and laboratory studies. A major focus in the past year has been on Kaposi's sarcoma and its associated DNA virus, HHV8. VEB researchers reported that multiple lesions of this tumor share the same clonal origin, further establishing Kaposi's sarcoma as a true malignant neoplasm. To clarify discrepancies in reported seroepidemiology of HHV8 infection, we sent a blinded test panel to six leading laboratories and found poor agreement among current HHV8 antibody assays, particularly for sera from normal blood donors. In a collaborative study, HHV8 seropositivity was found to be positively associated with measures of sexual activity, such as frequency of receptive anal intercourse. These studies indicate that serologic assays are contributing to epidemiologic investigations of HHV8, but are as yet inadequate for determining infection prevalence in individuals at low risk for Kaposi's sarcoma. The AIDS-Cancer Match Registry continues to contribute to our understanding of the spectrum of AIDS malignancies, and recent analyses identify seminoma, multiple myeloma, and brain cancer as increased in incidence in patients with AIDS. A similar analysis of U.S. death registrations identified several additional HIV-associated tumors with lower relative risk, although brain cancer was not increased in that study. Among reported anal cancer cases in San Francisco men age 25-54, approximately half were associated with AIDS, but the relative risk (if any) appears to be small in comparison to the relative risk associated with male homosexuality. Circulating lymphocytes with the Burkitt's lymphoma-associated t(8;14) translocation were found to be increased with duration of HIV infection, whereas the follicular lymphoma-associated t(14;18) translocation was not increased in HIV infection.